The invention relates to a method of manufacturing a semiconductor device, in which at least one semiconductor element, but preferably a large number of semiconductor elements, are provided, at a first connecting region extending in a first plane, with a first connecting conductor and, at a second connecting region extending in a second plane opposite the first plane, with a second connecting conductor, whereafter the semiconductor element is surrounded with a protective envelope, the semiconductor element being arranged between a first and a second plate of a conductive material, the first plate being provided with an opening and the semiconductor element being electroconductively secured with its first connecting region to a part of the first plate adjoining the opening, and the first connecting conductor being formed from the part of the first plate adjoining the opening, and the semiconductor element being electroconductively secured with its second connecting region to a part of the second plate.
Such a method is known from United States patent specification U.S. Pat. No. 5,506,174, published on Apr. 9, 1996. In said document, a description is given of how a number of semiconductor elements, such as diodes, are soldered between two metal plates. The two connecting conductors of a diode are formed from strip-shaped parts of the plates which are secured to the connecting regions of the diodes. The semiconductor elements are provided with a protective housing from which the connecting conductors project at two opposite sides. To obtain an individual semiconductor device with a semiconductor element, the redundant parts of the two plates are removed. To render the semiconductor device suitable for so-called surface mounting, the connecting conductors on either side of the semiconductor element are bent downwards.
A drawback of the known method resides in that the resultant semiconductor device is insufficiently reliable. Another drawback is that the method is relatively complicated.
It is an object of the invention to provide a method which results in very reliable devices, and which is easy to implement.
To achieve this, a method in accordance with the invention is characterized in that the part of the second plate to which the semiconductor element is secured is electroconductively secured to a further part of the first plate which adjoins the opening, which further part is situated opposite the part of the first plate from which the first connecting conductor is formed and from which the second connecting conductor is formed. In this manner, a semiconductor device is obtained in a simple and reliable manner, which semiconductor device can suitably be used for surface mounting. This can be attributed to the fact that the first and the second connecting conductor are now situated next to one another in the plane of the first plate. After the protective envelope has been provided, the two connecting conductors no longer have to be bent, which has a favorable effect on the reliability of the protective envelope. In addition, during the manufacture, the second connecting conductor is firmly fixed because it is secured to the second plate (of which it forms part) but also because it is secured to both the semiconductor element and to a further part of the first plate. This means that also upon providing the protective envelope, the device is better resistant to the concomitant forces exerted on the device. A further important additional advantage of the device thus obtained resides in that the cooling of the semiconductor element, particularly via the second connecting conductor, is improved because this connecting conductor, at least the end portion thereof, has a thickness which corresponds to the sum of the thicknesses of both plates. This, among other reasons, renders the method in accordance with the invention particularly suitable for the manufacture of semiconductor devices with a semiconductor element which has to be operated at a high voltage and/or high power.
In a first modification of the method in accordance with the invention, the part of the second plate which is electroconductively secured to the semiconductor element is provided, at the location of the further part of the first plate, with a projection the height of which is approximately equal to the thickness of the semiconductor element. In this variant, bending of the part of the second plate which is secured to the semiconductor element and to the further part of the first plate can be entirely dispensed with. In a preferred modification of this variant, the semiconductor element is provided with the protective envelope by providing the material of the envelope between both plates. The individual semiconductor device can then be obtained by cutting the first and second plates through as well as the intermediate protective envelope in two mutually substantially perpendicular directions, the operation being performed by cutting through the opening at two sides of the semiconductor element. By cutting through the opening at two sides of the semiconductor element, it is achieved that the first and the second connecting conductor no longer contact each other. One of the two directions in which cutting is performed may alternatively be chosen so that cutting takes place through the above-mentioned projection, so that two adjacent semiconductor elements can make use of a single projection which provides both with (a part of) the second connecting conductor.
In a preferred embodiment of a method in accordance with the invention the part of the second plate which is electroconductively secured to the semiconductor element is partly cut from the second plate and partly bent from the second plate over a distance which is approximately equal to the thickness of the semiconductor element minus the thickness of the second plate. Said bending operation can be readily performed during the manufacture of the second plate and, in addition, does not have the drawbacks of the above-mentioned method in accordance with the prior art. Preferably, the degree to which the part of the second plate is bent outside the plane of the second plate does not exceed three times the thickness of the material. By virtue thereof, the second plate can be manufactured readily and reliably. In practice, the material thickness is for example 0.2 mm, so that 0.6 mm is three times the thickness of the material. In connection therewith, the thickness of the element preferably does not exceed 0.6 mm.
Preferably, the first plate is provided with a blank which comprises the opening and which substantially completely surrounds the part of the first plate to which the semiconductor element is secured and the further part of the first plate, and the second plate is provided with a blank which substantially completely surrounds the part of the second plate which is electroconductively secured to the semiconductor element and to the further part of the first plate. The part and the further part of the first plate and the part of the second plate are preferably each connected by means of two bridges to the rest of the first plate. This too can be readily achieved in the course of the manufacture of both plates. To finally unlink the individual semiconductor device from the two plates, these bridges can be cut through or broken through. In a favorable modification, the part and the further part of the first plate are each connected by means of three bridges to the rest of the first plate, two bridges being formed so as to adjoin the opening and the third bridge being formed opposite the opening. Consequently, the shape of the opening approximately resembles the shape of a channel, thus enabling the material of the protective envelope to be readily fed to the semiconductor element and between the first and the second connecting conductor.
A method in accordance with the invention can particularly suitably be used to simultaneously manufacture a large number of devices. This can be achieved by positioning the semiconductor elements in a one or two-dimensional array between the plates. Using an array of 70 by 20 semiconductor elements, 1400 devices can be simultaneously manufactured.
The provision of the protective envelope can be advantageously carried out, particularly in a variant of the above-described embodiment, in the following manner: first of all, the redundant parts of the second plate are removed by cutting or breaking through the bridges connecting the part of the second plate to the second plate. Subsequently, the first plate, on which the semiconductor elements with the part of the second plate are present, is provided with a matrix comprising chambers accommodating the semiconductor elements, and comprising channels leading to said chambers. Via these channels, a synthetic resin, such as epoxy, is supplied to the semiconductor elements by means of an injection molding process, around which semiconductor elements a protective envelope corresponding to the chambers is formed. Finally, after removing the matrix, individual semiconductor devices are obtained by removing the redundant parts of the first plate and the redundant synthetic resin parts corresponding to the channels in the matrix.
These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment(s) described hereinafter.
In the drawings: